Sponsor Message:
Aviation Technical / Operations Forum
My Starred Topics | Profile | New Topic | Forum Index | Help | Search 
787 Laminar Flow Nacelles  
User currently offlineFaro From Egypt, joined Aug 2007, 1533 posts, RR: 0
Posted (4 years 7 months 2 weeks 12 hours ago) and read 11580 times:

In this presentation, under the following link (click: Visionary Design --> Aerodynamics --> Next --> Next = "Laminar Flow Reduces Drag"):

http://www.newairplane.com/787/design_highlights/

Boeing talks of laminar flow being maintained over a greater proportion of the 787 nacelle than in existing installations (ie, mainly on the nacelle leading edges and a little behind). How is this achieved, any suction integrated in the set-up? Surely it's only a question of materials so that laminar flow nacelles leading edges should theoretically be retrofit-able to existing airliners too. When can we expect to see this?

Also, why are the nose-end of the 787 and the wing/empannage leading edges not similarly laminar-flowed?

Faro

[Edited 2009-12-11 04:11:22]


The chalice not my son
19 replies: All unread, jump to last
 
User currently offlineOly720man From United Kingdom, joined May 2004, 6682 posts, RR: 11
Reply 1, posted (4 years 7 months 2 weeks 6 hours ago) and read 11494 times:



Quoting Faro (Thread starter):
How is this achieved, any suction integrated in the set-up?

Most likely the shape.

Very many moons ago RR did a lot of work at the lab I worked in on natural laminar flow and suction to improve engine nacelles. From what I remember the leading edge was a hyperellipse, giving a flatter front face than the usual squared relation for an ellipse would give.

Suction does work, but there are plenty of associated issues, not least the possibility of the holes getting blocked by dirt, dead insects, water, etc, and the pump and pipework losses associated with the suction system. Because the surface area of a nacelle is quite small in relation to the total surface area of the aircraft, savings using suction are quite marginal. If suction is going to be used it's most likely to appear on flying wings where its contribution will be more significant. But there will be certain operational issues that'll need to be overcome like what happens if it stops or there's a gradual deterioration in performance.

The historical problem with using suction was getting the suction distributed. The technique was tried in the late 40's with sintered porous materials, but not too successfully. It was only with the development of laser drilling where very small holes (0.2mm diam or less) could be produced in a surface quickly and easily, that suction techniques were successful. One of the problems with suction was the hole size itself. In earlier attempts with manually drilled holes, the diameter was such that suction caused local "plug hole" effects where the flow being sucked through the surface formed a jet structure that generated a wake and turbulence. With much smaller holes, the suction is felt very close to the surface and it's only the boundary layer immediately next to the surface that's removed.



wheat and dairy can screw up your brain
User currently offlineJetmech From Australia, joined Mar 2006, 2684 posts, RR: 53
Reply 2, posted (4 years 7 months 1 week 6 days 14 hours ago) and read 11355 times:



Quoting Faro (Thread starter):



Quoting Oly720man (Reply 1):
Most likely the shape.

I suspect that shape would have a lot to do with it. One way to promote laminar boundary layers is to produce a beneficial static pressure gradient along the surface in question. This pressure gradient would be one where the static pressure decreases as one moves along the surface.

On wings for example, such a pressure gradient generally exists from the leading edge to some region near the thickest point of the airfoil section. If one moves the thickest part of the airfoil aft, it is possible to extend the advantageous pressure gradient along a greater portion of the surface, and thus, provide conditions more conducive to a laminar boundary layer.

IIRC, this is what NACA did to produce the 6 series of airfoil sections, where the main advantage was a greater extent of laminar flow. I suspect Boeing may have done a similar thing with the 787 nacelle by moving the thickest part aft. Also, I seem to remember that Boeing uses a special paint on the nacelle to assist in maintaining the laminar boundary layer.

Regards, JetMech



JetMech split the back of his pants. He can feel the wind in his hair.
User currently offlineFaro From Egypt, joined Aug 2007, 1533 posts, RR: 0
Reply 3, posted (4 years 7 months 1 week 4 days 13 hours ago) and read 10975 times:



Quoting Oly720man (Reply 1):
Quoting Faro (Thread starter):
How is this achieved, any suction integrated in the set-up?

Most likely the shape.



Quoting Jetmech (Reply 2):
I suspect that shape would have a lot to do with it.

In that case, A, B and other manufacturers should be working on laminar flow nacelle mods for existing types, should they not? Seems an easy, elegant way to improve fuel burn. Is this the case?

Faro



The chalice not my son
User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 4, posted (4 years 7 months 1 week 3 days 21 hours ago) and read 10847 times:



Quoting Faro (Reply 3):
In that case, A, B and other manufacturers should be working on laminar flow nacelle mods for existing types, should they not? Seems an easy, elegant way to improve fuel burn. Is this the case?

Recertifying a nacelle is not trivial...I'm not sure the savings would be enough to offset the cost of development (clean sheet designs don't have this problem because they have to pay the design and cert costs anyway).

Tom.


User currently offlineFaro From Egypt, joined Aug 2007, 1533 posts, RR: 0
Reply 5, posted (4 years 7 months 1 week 3 days 16 hours ago) and read 10812 times:



Quoting Tdscanuck (Reply 4):
Recertifying a nacelle is not trivial...I'm not sure the savings would be enough to offset the cost of development (clean sheet designs don't have this problem because they have to pay the design and cert costs anyway).

Even if you are only re-designing the nacelle leading edges to hyper-elliptical shape? I'm no expert but would have thought that this would be a minor design/certification effort. After all, we're only talking about laminar flow over perhaps one seventh of the nacelle lengthwise.

Faro



The chalice not my son
User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 6, posted (4 years 7 months 1 week 2 days 21 hours ago) and read 10706 times:



Quoting Faro (Reply 5):
Even if you are only re-designing the nacelle leading edges to hyper-elliptical shape? I'm no expert but would have thought that this would be a minor design/certification effort. After all, we're only talking about laminar flow over perhaps one seventh of the nacelle lengthwise.

Yeah, but you're talking about (potentially) altering the engine inlet flow. I don't see the regulators accepting that one by analysis. You'd also have to cover nacelle cooling and ice protection over again (and maybe fireextinguishing as well), although I can see all those maybe being done by analysis.

Tom.


User currently offlineOly720man From United Kingdom, joined May 2004, 6682 posts, RR: 11
Reply 7, posted (4 years 7 months 1 week 2 days 14 hours ago) and read 10636 times:

Looking at other articles, it does seem that there are very tight profile tolerances on the nacelle inlet

http://www.flightglobal.com/articles...or-787s-in-bid-to-reduce-fuel.html

It will be interesting to see how it performs in service and whether abrasion will have any impact on performance.

I also see that it's Boeing rather than RR who have taken charge of this part of the design.


Laminar conditions are generally hard to achieve and maintain, and Boeing has put considerable effort into this design aspect to offset the drag of the 787’s extra large bypass engines at a time of rising fuel costs.


I suppose I assumed that it was the engine manufacturer who was responsible for the nacelle, with some input from the aircraft manufacturer. Or perhaps RR produced a nacelle with the potential for NLF and Boeing looked after the implementation of it in service.

I think the main problem with retrofitting new inlets is that they would to be longer than the inlets they'd be replacing, so there'd be no surface steps or gaps to trip the boundary layer. It wouldn't be a matter of unbolting one and fitting the other.

Comparing with, say, the A330


View Large View Medium
Click here for bigger photo!

Photo © Guiqi2006


View Large View Medium
Click here for bigger photo!

Photo © Royal S King



I'm assuming that the part of the engine aft of the natural metal inlet on the A330, is a different piece, not the natural metal painted in company colours, and it's the small surface imperfections here that would trip a laminar boundary layer, if it was still laminar.



wheat and dairy can screw up your brain
User currently offlineFaro From Egypt, joined Aug 2007, 1533 posts, RR: 0
Reply 8, posted (4 years 7 months 1 week 2 days 13 hours ago) and read 10624 times:



Quoting Oly720man (Reply 7):
I think the main problem with retrofitting new inlets is that they would to be longer than the inlets they'd be replacing, so there'd be no surface steps or gaps to trip the boundary layer. It wouldn't be a matter of unbolting one and fitting the other.



Quoting Tdscanuck (Reply 6):
Yeah, but you're talking about (potentially) altering the engine inlet flow. I don't see the regulators accepting that one by analysis.

 checkmark 
Absolutely correct, yes. My impression that a easy retrofit was possible was triggered by the misperception of the 787's size and the size of the nacelles. It's sometimes hard to believe that it's practically as long as the A332, probably due to the 787's wider fuselage and bulbous nacelles. Proportion-wise, one's first impression is that it's 739-esque...

Faro



The chalice not my son
User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 9, posted (4 years 7 months 1 week 1 day 19 hours ago) and read 10486 times:



Quoting Oly720man (Reply 7):

I also see that it's Boeing rather than RR who have taken charge of this part of the design.

That's normal. The outer mold lines of the whole aircraft is usually in the hands of the airframer, not the engine maker.

Quoting Oly720man (Reply 7):
I suppose I assumed that it was the engine manufacturer who was responsible for the nacelle, with some input from the aircraft manufacturer.

RR has a history of providing complete propulsion packages (engine/nacelle/thrust reverser), but they're the exception. Even in that case, the airframer will have huge say in the outer mold lines (i.e. the aerodynamics).

Tom.


User currently offlineBaroque From Australia, joined Apr 2006, 15380 posts, RR: 59
Reply 10, posted (4 years 7 months 1 week 1 day 16 hours ago) and read 10461 times:

Not disputing that precise details of the lips might not make a difference but it raises (for me) the question of how much is lost with the "squashed" nacelles on the later 737s? While busy, anyone care to explain the squared off nacelles for many high speed jets - I don't suppose they have square fans and turbines!!  duck   duck 

User currently offlineOly720man From United Kingdom, joined May 2004, 6682 posts, RR: 11
Reply 11, posted (4 years 7 months 1 week 1 day 14 hours ago) and read 10446 times:



Quoting Baroque (Reply 10):
the squared off nacelles for many high speed jets

do you mean the rectangular inlets on combat aircraft?


View Large View Medium
Click here for bigger photo!

Photo © Kim Jong Hwan



The short answer is shockwaves in supersonic flight. The intake is angled so that an oblique shockwave is generated from the upper lip and this helps create the pressure needed at the engine inlet, and a subsonic flow. You don't really want supersonic flows in inlets because they create shockwaves that generate high pressure variations. I think the only exception to this was Concorde that had the intake flow path profiled so that it deliberately created shocks to increase the engine pressure ratio. But Concorde was a lot longer and there was the space to do it. On combat aircraft there's not the room to do this.

Why rectangular? Well the F15 inlet, and others can be angled downwards


View Large View Medium
Click here for bigger photo!

Photo © Gerard Helmer



and having a rectangle makes this easier.

The rectangular inlet on the F15 and others, serves the same shock generating purpose as the cone/half cone/quarter cone on other aircraft



View Large View Medium
Click here for bigger photo!

Photo © Thomas P. McManus



View Large View Medium
Click here for bigger photo!

Photo © SENAND Matthias



View Large View Medium
Click here for bigger photo!

Photo © Ng Wai Ping




wheat and dairy can screw up your brain
User currently offlineBaroque From Australia, joined Apr 2006, 15380 posts, RR: 59
Reply 12, posted (4 years 7 months 1 week 1 day 11 hours ago) and read 10417 times:



Quoting Oly720man (Reply 11):
Quoting Baroque (Reply 10):
the squared off nacelles for many high speed jets

do you mean the rectangular inlets on combat aircraft?


Yes, and I know why they are rectangular, what I wondered was what does that do for fuel consumption subsonic which is where the ALL spend MOST of their time. Alvays ze difficult qvestuns!


User currently offlineOly720man From United Kingdom, joined May 2004, 6682 posts, RR: 11
Reply 13, posted (4 years 7 months 1 week 1 day 9 hours ago) and read 10398 times:

Ah, OK.

I'm not sure that anyone has gone to the trouble of investigating the effects of different intake shapes on engine fuel consumption, though there will be effects on the overall aerodynamics of the aircraft. There aren't any planes I can think of that have different intake shapes apart from the F/A-18 which went from oval on early versions to square with the Super Hornet. I once saw an early wind tunnel model of the Tornado that had side intakes like a Mirage and, presumably, studies showed that the rectangular ones were better.

As long as the intake provides the correct pressure distribution and flow rate to the front face of the engine then the engine's happy and the intake, to some extent, is irrelevant. After that any effects are external aerodynamics/drag which will have an impact on fuel consumption



wheat and dairy can screw up your brain
User currently offlineJetMech From Australia, joined Mar 2006, 2684 posts, RR: 53
Reply 14, posted (4 years 7 months 1 week 20 hours ago) and read 10299 times:



Quoting Faro (Reply 8):
easy retrofit

I suspect that one would need to pay attention to a fair portion of the nacelle aft of the lip to achieve a greater extent of laminar flow.

If the Reynolds number is low enough, the boundary layer may possibly remain as a laminar one for the entire distance over which it interacts with the surface of the object. As one increases the Reynolds number, the boundary layer will likely transition from laminar to turbulent at some point on the surface, with this transition point moving further forward as the Reynolds number continues to increase.

At the high Reynolds numbers encountered in actual flight, the region of the surface with a laminar boundary layer would most likely be very small. Thus, to extend the surface region subjected to a laminar boundary layer at high Reynolds numbers requires much careful design to achieve, most probably with careful shaping and surface quality.

Any slight disturbance such as steps or irregularities in the surface, dust, insects, dirt and even vibration can be enough to initiate transition and cause the boundary layer to "prematurely" turn from laminar to turbulent at elevated Reynolds numbers.

Apparently, laminar boundary layers can remain so even in the presence of large disturbances if the Reynolds number is low enough. Laminar boundary layers can also remain so at very high Reynolds numbers, but one then needs to take extreme measures to ensure the homogeneity of the fluid, a disturbance free environment as well as a very smooth and carefully shaped object

http://en.wikipedia.org/wiki/Reynolds_number

Regards, JetMech



JetMech split the back of his pants. He can feel the wind in his hair.
User currently offlineFaro From Egypt, joined Aug 2007, 1533 posts, RR: 0
Reply 15, posted (4 years 7 months 1 week 15 hours ago) and read 10261 times:



Quoting JetMech (Reply 14):
smooth and carefully shaped object

Thanx JetMech for the detailed feedback re Reynolds. One thing that just stuck me though: those 787 nacelles leading edges are not bright and shiny metal. Does this mean that matte surfaces can somehow also be hyper-smooth? Some new technology involved here, funky coatings perhaps?

Faro



The chalice not my son
User currently offlineStitch From United States of America, joined Jul 2005, 30532 posts, RR: 84
Reply 16, posted (4 years 7 months 1 week 8 hours ago) and read 10208 times:
Support Airliners.net - become a First Class Member!



Quoting Faro (Reply 3):
In that case, A, B and other manufacturers should be working on laminar flow nacelle mods for existing types, should they not?

CFM has developed an elongated nacelle that will house the CFM56-7B Evolution engine when it starts testing. The nacelle has been flown on a 737-900ER, but it looks like all the benefits will come from the engine itself, not the nacelle.


User currently offlineAerodog From United States of America, joined Jun 2006, 118 posts, RR: 0
Reply 17, posted (4 years 7 months 1 week 5 hours ago) and read 10173 times:

Slightly off topic but the engine pylons appear to be yawed inboard at the leading edge.

Am I seeing something that isn't there or has Boeing canted them to streamline the pylons with the airflow around the fuselage?


User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 18, posted (4 years 7 months 6 days 19 hours ago) and read 10101 times:



Quoting Faro (Reply 15):
those 787 nacelles leading edges are not bright and shiny metal. Does this mean that matte surfaces can somehow also be hyper-smooth?

I think they're titanium, which is almost never shiny unless you really work at it. Provided the scale of the roughness is smaller than the boundary layer thickness, which isn't particularly hard, the surface looks "smooth" to the airflow.

Quoting Aerodog (Reply 17):
Slightly off topic but the engine pylons appear to be yawed inboard at the leading edge.

Am I seeing something that isn't there or has Boeing canted them to streamline the pylons with the airflow around the fuselage?

It appears to be real. You can see the tilt and cant on the scaled drawings:
http://www.boeing.com/commercial/airports/acaps/787sec9.pdf

I can't think of any reason you wouldn't align them with the local flow, and the flow should be slightly outboard due to both displacement by the forward fuselage and induced flow from the wings.

Tom.


User currently offlineFaro From Egypt, joined Aug 2007, 1533 posts, RR: 0
Reply 19, posted (4 years 7 months 6 days 14 hours ago) and read 10079 times:



Quoting Tdscanuck (Reply 18):
Quoting Faro (Reply 15):
those 787 nacelles leading edges are not bright and shiny metal. Does this mean that matte surfaces can somehow also be hyper-smooth?

I think they're titanium, which is almost never shiny unless you really work at it. Provided the scale of the roughness is smaller than the boundary layer thickness, which isn't particularly hard, the surface looks "smooth" to the airflow.

They are in fact aluminium (refer above link in thread opener: click on Visionary Design --> Composites). This Composites page has a materials-composition diagram for the 787 which shows that the only titanium part is the tail cone.

My money is on a funky coating on the aluminium nacelle leading edge surface...

Faro



The chalice not my son
Top Of Page
Forum Index

Reply To This Topic 787 Laminar Flow Nacelles
Username:
No username? Sign up now!
Password: 


Forgot Password? Be reminded.
Remember me on this computer (uses cookies)
  • Tech/Ops related posts only!
  • Not Tech/Ops related? Use the other forums
  • No adverts of any kind. This includes web pages.
  • No hostile language or criticizing of others.
  • Do not post copyright protected material.
  • Use relevant and describing topics.
  • Check if your post already been discussed.
  • Check your spelling!
  • DETAILED RULES
Add Images Add SmiliesPosting Help

Please check your spelling (press "Check Spelling" above)


Similar topics:More similar topics...
Leahy: Boeing 787 Single Barrels "A Bridge To Far" posted Wed Nov 4 2009 00:52:06 by Keesje
Thoughts On The 787 Wingox... posted Tue Oct 27 2009 23:06:06 by ElpinDAB
Cabin Width On 787 posted Tue Sep 15 2009 14:46:37 by Propilot83
787 Fuselage Production posted Tue Jun 9 2009 09:05:52 by B737200
RR Recovers Trent Fuel Burn Margin For 787 posted Sun Apr 5 2009 06:16:37 by Rheinbote
787 De-Icing posted Tue Feb 17 2009 12:33:13 by Nycbjr
So, What Does Mach 6 Flow Really Look Like? posted Wed Feb 11 2009 22:24:50 by Tdscanuck
Boeing 787 Dreamliner Cabin, How Silent / Noisy? posted Wed Feb 4 2009 04:34:43 by Keesje
Boeing 787 Engines posted Thu Jan 15 2009 09:06:48 by Legoguy
787 Wings posted Tue Nov 25 2008 10:29:09 by C5LOAD

Sponsor Message:
Printer friendly format